Ophthalmic lenses, such as spectacles, contact lenses and intraocular lenses, may be configured to provide both spherical and cylindrical power. An intraocular lens (IOL) is a lens implanted in the eye used to treat cataracts or myopia. IOLs may be used for restoring visual performance after a cataract surgery or other ophthalmic procedure in which the natural crystalline lens is replaced with or supplemented by implantation of an IOL. A variety of different types of IOLs are currently available, including monofocal and multifocal IOLs, phakic IOLs and piggyback IOLs (i.e. IOLs implanted in an eye already having an IOL).
Toric lenses typically have at least one surface that can be described by an asymmetric toric shape having two different primary curvature values in two orthogonal axes, wherein the toric lens is characterized by a “low power meridian” with a constant power equal to the base spherical power and an orthogonal “high power meridian” with a constant power equal to the base spherical power plus the cylinder power of the lens. Intraocular lenses, which are used to replace or supplement the natural lens of an eye, may also be configured to have a cylinder power for reducing or correcting the astigmatic effect of the cornea or eye.
One significant issue is the cost and/or time needed to develop and evaluate new IOL designs. Current methods and systems for measuring IOL image quality includes modular transfer function (MTF) measurement using an MTF bench for measuring the optical transfer function by its module and phase of an IOL. The MTF is the modulation or contrast of the image formed by the system or IOL for various spatial frequencies or various size targets. Frequently, black and white bars with 100% contrast are used as the targets. As the size of the target decreases, the system's ability to maintain high contrast decreases.
Such an MTF bench is typically used to measure the image quality with symmetrical features. That is, the modular transfer function is radially symmetrical. For an asymmetrical image quality like a toric lens, the MTF bench measures the X and Y meridians of the lens individually by forcing the image being evaluated be aligned with an X or Y meridian.
This may not be convenient and accurate enough to reflect the true image quality, especially in asymmetrical lenses, such as an IOL that may provide such as a highly asymmetric IOL or freeform design like the toric IOL with extended tolerance of astigmatic effects.
Therefore measuring the image quality by the current system design is not enough to capture the best image quality of the system (such an eye). Therefore, a method and system that can measure the meridian dependent image quality is needed to objectively and fully evaluate the image quality of asymmetrical IOLs including asymmetrical toric IOLs like extended tolerance astigmatism (“ETA”) IOLs. Examples of such ETA IOLs are described in U.S. Patent Application No. 63/312,321 (filed Mar. 23, 2016); 63/312,338 (filed Mar. 23, 2016); and 62/363,428 (filed Jul. 18, 2016), which are each hereby incorporated by reference for all purposes as if fully set forth herein.